Method and arrangement for performing low-temperature grinding operations in a vibrating mill

ABSTRACT

Low-temperature grinding operations are performed in the horizontal and longitudinal tubular grinding chambers of a vibrating mill by introducing the material to be ground at one end of the grinding chambers introducing at least at one point of the grinding chambers adjustable amounts of a refrigerant-for example liquid nitrogen-above the surface of the material to be ground in the grinding chambers, and arranging a thermometer probe at each point of introduction at a point spaced ahead of the points of refrigerant introduction when considering the direction of travel of the material to be ground lengthwise in said grinding chamber, said thermometer probe being used for adjusting the amount of refrigerant introduced into said grinding chamber to maintain the temperature in the latter at a predetermined level.

Waited States Patent 1 Haas et al.

[54] METHOD AND ARRANGEMENT FOR PERFORMING LOW-TEMPERATURE GRINDINGOPERATIONS IN A VIBRATING MILL [75] Inventors: Helmut Haas, Cologne;Helmut Siedler, Essen, both of Germany [73] Assignees:Klockner-Humboldt-Deutz Aktiengesellschaft, Koln; Air Products GmbH,Dusseldorf, Germany [22] Filed: Dec. 14, 1971 [21] Appl. No.1 207,912

[58] Field of Search ..241/15, l7, 18, 30, 241/38, 41-44, 65,153, DIG.13

[5 6] References Cited UNITED STATES PATENTS 3/1959 Jarvis ..241/65X9/1966 Reiners ..24l/l53 1 May 22, 1973 FOREIGN PATENTS OR APPLICATIONS710,320 5/1965 Canada ..24l/65 Primary Examiner-Donald G. KellyAttorney- Hill, Sherman, Meroni et al.

[57] ABSTRACT Low-temperature grinding operations are performed in thehorizontal and longitudinal tubular grinding chambers of a vibratingmill by introducing the material to be ground at one end of the grindingchambers introducing at least at one point of the grinding chambersadjustable amounts of a refrigerant-for example liquid nitrogen-abovethe surface of the material to be ground in the grinding chambers, andarranging a thermometer probe at each point of introduction at a pointspaced ahead of the points of refrigerant introduction when consideringthe direction of travel of the material to be ground lengthwise in saidgrinding chamber, said thermometer probe being used for adjusting theamount of refrigerant introduced into said grinding chamber to maintainthe temperature in the latter at a predetermined level.

6 Claims, 1 Drawing Figure METHOD AND ARRANGEMENT FOR PERFORMINGLOW-TEMPERATURE GRINDING OPERATIONS IN A VIBRATING MILL The inventionrelates to a method for performing low-temperature grinding operationsin a vibrating mill by the addition of refrigerants into the grindingspace.

The German Auslegeschrift DAS l 004 460 discloses a device forcold-grinding of solid, viscous materials in which the materials to begroundfor instance, thermoplastic resinsprior to the introduction in thegrinding device are conveyed through a cooling tub filled with liquidnitrogen. In this nitrogen-filled tab the materials to be ground aremade brittle and are then conducted into the grinding device. For thecooling of the feed lines and of the grinding space are employed thevapors which are produced in the liquid bath of the cooling tub.

It has now been discovered that this known method for cooling thegrinding device is not sufficient and that in particular in afine-grinding operation taking place in a vibrating mill, certainamounts of heat are released which require another form of cooling ofthe material to be ground in the grinding chamber. This is particularlytrue for materials whose point of embrittlement lies only about to 30 C.above the temperature of the refrigerant.

It is an object of the invention to overcome these disadvantages of thisknown method in that the refrigerant is introduced above the surface ofthe material to be ground in the grinding chamber by employing at leastone injection nozzle provided with a regulating valve, whereby theamount of refrigerant to be injected by each injection nozzle isdetermined by a thermometer probe which, when viewed in axial directionof the tubular grinding chamber and from the point of introduction ofthe material to be ground, is arranged in spaced relation ahead or infront of the associated injection nozzle. This procedure on one handpermits the maintenance of the required grinding temperature within thegrinding chamber in spite of the amounts of heat which are produced bythe grinding operation. On the other hand, however, the low temperatureof the material to be ground when it enters the grinding space as a rulerequires only small amounts of refrigerants for the maintenance of thegrinding temperature, but during a continuous injection the consumptionof refrigerants would be comparatively high, and the regulation of theamount of refrigerant is only possible by measuring the temperature inthe grinding chamber. By making use of the fact that during continuouslyoperating vibrating mills the material to be ground travels from thepoint of introduction along the grinding chamber in the direction towardthe discharge point, and that also in view of the movement of thegrinding bodies and the movement of the material to be ground within thegrinding tube causes the injected refrigerant to move in the samedirection, the regulation of the amount of injected refrigerant requiresa temperature measurement by means of a temperature probe, whichlatterviewed in the axial direction of the grinding chamber and from thepoint of introduction of the material to be groundis arranged in frontof the associated injection point. In this manner it is possible in asimple manner to determine the temperature rise along the length of thegrinding chamber by the released heat as a result of the grindingoperation, whereby then in each case within the range in rear of thepoint where the temperature is measured in relation to the temperaturemeasured at this point, additional amounts of refrigerant may beintroduced into the material to be ground in the subsequent part of thegrinding chamber without that the newly introduced amounts ofrefrigerants influence the temperature measurements.

In accordance with the invention, the method provides that eachtemperature probe in each instance by means of a regulator cooperateswith the adjusting device of the regulating valve of the associatedinjection nozzle. In view of this procedure, it is possible to obtainthe advantage of a continuous operation.

According to a preferred embodiment of the invention, the regulator isso constructed that the opening and closing, respectively, of theassociated regulating valve takes place in each instance when the upperor lower temperature limit, respectively, has been reached. It is ofadvantage when the regulator is provided with a so-called time elementwhich preferably closes the regulating valve already before reaching thelower temperature limit.

According to another object of the invention, the refrigerant is sprayedin liquid condition from above onto the exposed top surface of thematerial to be ground in the grinding chamber. This procedure has theadvantage that on one hand very simple spray nozzles may be employedwhich assure a good distribution of the refrigerant in the grindingchamber within the range of the injection location, while on the otherhand, the advantage is obtained that the helical movement of thematerial to be ground owing to the influence of the vibratory movementof the grinding chamber causes the refrigerant sprayed onto the uppersurface of the material to reach also the lower ranges of the filling ofthe material to be ground in the grinding chamber.

In the following will be described the method of the invention by way ofexample with reference to flow diagram of an embodiment illustrated inthe accompanying drawing.

Referring to the drawing, the two horizontally arranged grinding tubes 1and 2 are disposed in spaced relation vertically one above the other andare secured in a supporting frame 3 which is mounted to be vibrated andis also provided with means for vibrating it. The left-hand end of theupper grinding tube 1 is connected with a vertically extending feed pipe4 whose upper end is connected to a cooling device 5 in which thematerial to be ground is cooled. The two grinding tubes 1 and 2 areconnected with their right-hand ends with each other by a verticallydisposed connecting pipe 6 and the left-hand lower end of the grindingtube 2 is provided with a material discharge pipe 7 which conducts theground material into a collecting container 8.

The material to be ground is introduced by a sluiceway 9 into the upperend of the cooling device 5. Into this cooling device also extends adownwardly directed portion of a pipeline 10 which extends from aboveinto the filling of the material in the cooling device 5 and has at itslowermost end a system of nozzles which introduce a refrigerant-forinstance, fluid ni trogen-into the mass of material in the coolingdevice. The amount of nitrogen is determined by a thermometer probe 11connected with a regulator 12 which in turn cooperates with a regulatingvalve 13 arranged in the pipeline 10.

The cooled material to be ground is discharged from the cooling device 5into the pipe 4 which conveys the material into the grinding containercomprising a horizontally disposed longitudinal tube 1 closed at bothits ends.

Under the influence of the vibratory movement and the continuouslyintroduced material through the pipe 4, the individual particles of thematerial travel in the direction of the arrow 14 through the grindingcontainer 1 which is filled with grinding bodies. The ground materialpasses at the right-hand end of the grinding container 1 through thesmall apertures provided in a partition 15 which permits solely thepassage of ground material, while the grinding bodies remain in thegrinding chamber of the tube 1. The ground material is then conductedthrough the connecting pipe 6 into the grinding tube 2 which likewise isfilled with grinding bodies. In this grinding tube 2 the material to beground travels under the influence of the vibratory movement and theconstantly supplied ground material from the discharge end of theconnecting pipe 6 in the direction of the arrow 16 toward the dischargepipe 7 of the grinding tube 2 and from there into the collectingcontainer 8.

in order to compensate for the cold losses which occur during thegrinding operation which latter produces heat in spite of thearrangement of the insulating jackets on the grinding tubes, a nozzle 18introduces into the grinding chamber of the grinding tube 1 at a placeabove the surface 17 of the material to be ground additionalrefrigerant. At the place where this nozzle 18 enters the grindingchamber a thermometer probe 19 is arranged which by means of a regulator20 coop crates with a regulating valve 21 which is arranged ahead of theinjection nozzle 18 to the left thereof. The arrangement of theinjection nozzle 18 and of the thermometer probe 19 with respect to eachother is such that the injection nozzle 18 extends farther into thegrinding chamber than the thermometer probe 19 so that the measurementof the temperature is not influenced by the injected refrigerant.

The refrigerant which in the meantime has evaporated is withdrawn fromthe collecting container 8 and depending upon its temperature and amountis returned entirely or partly to the cooling device 5 for the purposeof primary cooling of the material in the cooling device 5.

Preferably the injection nozzle 18 is so constructed that therefrigerant is sprayed onto the surface 17 of the material to be groundand can enter this material while it performs a substantially helicalmovement which takes place in the direction of the arrow 14 and which iscaused by a circular oscillating movement directed at right angles tothe plane of the drawing.

Since depending upon the length of the grinding chamber and the periodof the time the material remains in the grinding chamber, the amount ofrefrigerant introduced at the point ofintroduction of the material isnot sufficient to keep the temperature in the grinding containerconstant, the invention provides that at a distance of about one half ofthe length of the grinding tube a second injection nozzle 22 is arrangedwhich sprays additional refrigerant onto the surface 17 of the materialto be ground in the grinding tube. For the purpose of regulating theamount of refrigerant with reference to the direction of movementindicated by the arrow 14, a thermometer probe 23 is arranged spaced infront of the second injection nozzle 22 and this thermometer probe 23 isconnected by its own regulator 24 with a corresponding regulating valve25 arranged in the supply pipe leading to the nozzle 22. In view of thefact that the thermometer probe 23 is arranged with reference to theaxial direction of movement of the material in front of the injectionnozzle 22, the rise in temperature in the first half of the grindingchamber, namely from the point of introduction in the range of theintroduction of the material up to about the center of the grindingchamber, may be regulated without being influenced by the amount ofrefrigerant sprayed by the nozzle 22 into the second half of thegrinding chamber.

The regulators 2t} and 23, respectively, are preferably constructed asso-called two-point regulators in which an upper and a lower temperaturevalue are adjusted, so that when the upper value of the temperature isreached the regulating valve 21 or 25 is opened, while upon reaching thelower limit value of the temperature the regulating valve 21 or 25 isclosed.

Each regulating circuit comprising a thermometer probe, a regulator, andadjusting valve, an injection nozzle and the grinding chamber mayadvantageously be modified in such a manner that by means of socalledtiming elements arranged within the regulators when the upper limitvalue of the temperature is reached, the injection valve is only openedfor a limited period of time so as to avoid that the regulating valvecloses only then when the lower limit value has been reached.Preferably, these timing elements are so constructed that during theclosure operation the injected amount is continuously reduced. In thismanner the temperature variations can be kept within the adjusted limitvalues. It is not required to drop the temperature below the lower limitvalue of the temperature because this would only cause an additionalamount of refrigerant. The so-called timing elements of the device whichis to be regulated is suitably adjustable concerning the opening timesof the valve.

The grinding tube 2 in which the final grinding operation takes place asthe grinding tube 1 is provided in similar manner with injectionnozzles, thermometer probes, regulators and regulating valves whichoperate in the same manner as these elements operate in the grindingtube 1.

In place of an automatic regulation, the thermometer probe may only beequipped with an indicating instrument. The operation of the regulatingvalves then takes place manually and if desired by remote control means.This last-named arrangement may then find application when in view ofthe size of the mill, the amount of the material to be ground, thequality of the insulation, etc., it is necessary to continuouslyintroduce a refrigerant into the grinding chamber so that only excessivevariations have to be controlled.

What we claim is:

1. Method for performing low-temperature grinding operations in ahorizontal and longitudinal grinding chamber of a vibrating mill,comprising introducing the material to be ground at one end of saidgrinding chamber and causing it to travel toward the other end,introducing at least at one point of said grinding chamber adjustableamounts of a refrigerant into said grinding chamber above the surface ofthe material to be ground therein, and arranging a thermometer probe ateach said point of refrigerant introduction at a point spaced ahead ofthe points of introduction of said refrigerant when considering thetravel direction of the material to be ground lengthwise in saidgrinding chamber, said thermometer probe being effective to adjust theamount of refrigerant introduced into said grinding chamber, so as tomaintain in said grinding chamber a predetermined temperature.

2. Method according to claim 1, in which each of said thermometer probesis connected by its own regulator with the adjusting means of anindividual regulating valve cooperating with means introducing a sprayof refrigerant into said grinding chamber at a particular point.

3. Method according to claim 1, in which each of said thermometer probesis connected by its own regulator with the adjusting means of anindividual regulating valve cooperating with means introducing a sprayof refrigerant into said grinding chamber at a particular point, saidregulator causing an opening and closing, respectively, of saidregulating valve upon reaching a predetermined upper or lowertemperature in said grinding chamber.

4. Method according to claim 1, in which each of said thermometer probesis connected by its own regulator with the adjusting means of anindividual regulating valve cooperating with means introducing a sprayof refrigerant into said grinding chamber at a particular 6 point, saidregulator being provided with a timing element which is effective toclose said regulating valve and continuously reduces the injection ofrefrigerant just prior to the reaching of the predetermined lowertemperature.

5. Method according to claim 1, in which said refrigerant is sprayed inliquid form onto the surface of the material to be ground in saidgrinding chamber.

6. An arrangement for performing low-temperature grinding operations,comprising a vibrating mill provided with a horizontally disposedgrinding tube, vibratory frame supporting said grinding tube, means forintroducing the material to be ground at one end of said grinding tube,nozzle means for spraying at least at one point of said grinding tubeadjustable amounts of a re frigerant onto the top surface of thematerial to be ground in said grinding tube, a thermometer probe foreach said nozzle means arranged at a point spaced ahead of said nozzlemeans when considering the direction of travel of the material to beground due to the vibrations of said grinding tube caused by saidvibratory frame, and means connecting said thermometer probe with nozzleadjusting means to cause said nozzle means to spray said adjustableamounts of refrigerant into said grinding tube so as to maintain withinthe latter a predetermined temperature.

1. Method for performing low-temperature grinding operations in ahorizontal and longitudinal grinding chamber of a vibrating mill,comprising introducing the material to be ground at one end of saidgrinding chamber and causing it to travel toward the other end,introducing at least at one point of said grinding chamber adjustableamounts of a refrigerant into said grinding chamber above the surface ofthe material to be ground therein, and arranging a thermometer probe ateach said point of refrigerant introduction at a point spaced ahead ofthe points of introduction of said refrigerant when considering thetravel direction of the material to be ground lengthwise in saidgrinding chamber, said thermometer probe being effective to adjust theamount of refrigerant introduced into said grinding chamber, so as tomaintain in said grinding chamber a predetermined temperature.
 2. Methodaccording to claim 1, in which each of said thermometer probes isconnected by its own regulator with the adjusting means of an individualregulating valve cooperating with means introducing a spray ofrefrigerant into said grinding chamber at a particular point.
 3. Methodaccording to claim 1, in which each of said thermometer probes isconnected by its own regulator with the adjusting means of an individualregulating valve cooperating with means introducing a spray ofrefrigeraNt into said grinding chamber at a particular point, saidregulator causing an opening and closing, respectively, of saidregulating valve upon reaching a predetermined upper or lowertemperature in said grinding chamber.
 4. Method according to claim 1, inwhich each of said thermometer probes is connected by its own regulatorwith the adjusting means of an individual regulating valve cooperatingwith means introducing a spray of refrigerant into said grinding chamberat a particular point, said regulator being provided with a timingelement which is effective to close said regulating valve andcontinuously reduces the injection of refrigerant just prior to thereaching of the predetermined lower temperature.
 5. Method according toclaim 1, in which said refrigerant is sprayed in liquid form onto thesurface of the material to be ground in said grinding chamber.
 6. Anarrangement for performing low-temperature grinding operations,comprising a vibrating mill provided with a horizontally disposedgrinding tube, vibratory frame supporting said grinding tube, means forintroducing the material to be ground at one end of said grinding tube,nozzle means for spraying at least at one point of said grinding tubeadjustable amounts of a refrigerant onto the top surface of the materialto be ground in said grinding tube, a thermometer probe for each saidnozzle means arranged at a point spaced ahead of said nozzle means whenconsidering the direction of travel of the material to be ground due tothe vibrations of said grinding tube caused by said vibratory frame, andmeans connecting said thermometer probe with nozzle adjusting means tocause said nozzle means to spray said adjustable amounts of refrigerantinto said grinding tube so as to maintain within the latter apredetermined temperature.